The study of dividing and non-dividing tetrathyridia using electron microscopy shows that the mode of multiplication by antero-posterior fission of these larvae is due to a particular tissue which is called the "apical massif". The apical massif is a part of the tegumental syncytium. It is located at the top of the scolex. It represents a polynucleated cell mass which has cytomorphogenetic power. During asexual multiplication, it differentiates into tegumental syncytium, sub-tegumental muscles, glycogen-storing parenchyma cells, and other cell types. Parts of it remain undifferentiated. The hypothetic origin of the apical massif is discussed. Longitudinal growth of the tetrathyridia occurs by invasion of migrating cells into the tegumental syncytium. These cells also originate from the apical massif. During asexual multiplication and longitudinal growth, filamentous microtriches are synthesized below the plasmalemma of the superficial cytoplasm of the tegumental syncytium. It is supposed that the blade-like microtriches derive from filamentous forms.

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Seven different types of wall pore and terminal pore sensilla of larvae, nymphs, male and female of A. variegatum are described. Wall pore single-walled (wp-sw) sensilla A and B have numerous plugged pores with pore tubules. Types A and B differ mainly in the thickness and the structure of the shaft wall. Wall pore double-walled (wp-dw) sensilla A and B have continuous longitudinal grooves. Vase-shaped radial canals lead from the central cavity to the grooves. Types A and B differ in the structure of the base and in the mode of innervation. Wp-dw/C sensilla have interrupted grooves and fine, somewhat twisted radial canals. Terminal pore (tp) sensilla have a terminal pore opening which is slit-like in type A and starfish-shaped in type B. Type A has two lumina while type B possesses a single lumen and a striking electrondense intermediate layer in the tip. Wall pore and terminal pore sensilla are supposed to be mono-or multimodal chemosensory hairs.